The p/n looks to be 4094404. No idea where you might find new clips. I checked the places I could think of (Clips and Fasteners, Parts Voice, Ebay, Mr G's, etc) and came up with zip.
There's usually 2 types of clips back there. Plastic ones where the metal is and metal ones with a stud that goes into the rubber bumper filler bit. If that's the case take the nut off from the back of the bumper filler and then gently pull up on the trim and either pull the top out with your fingers or pry it off with a screw driver and it'll pop off without damaging anything.
Look in the trunk first to make sure there aren't studs or anything else holding that part on either or else you will damage something prying at it.
I was doing a little work on it and noticed that the trim was hanging down. The double sided tape the previous owner blessed it with had come loose. There are two sets of studs closer to the wheel well (top and bottom) and the metal clip on the bumper filler. : : @